The present invention relates to a driver device which causes a vibrator to produce driving vibrations, a physical quantity measuring device (e.g. vibrating gyroscope) using the driver device, an electronic instrument, and the like.
Gyroscopes are classified as a rotating gyroscope, a vibrating gyroscope, and the like depending on the method of detecting the force applied to an object. In particular, a vibrating gyroscope is considered to be advantageous for reducing size and cost from the viewpoint of the constituent elements and the like. As a vibrating gyrosensor which detects an angular velocity applied to an object, a piezoelectric vibrating gyrosensor is known which excites a crystal or a piezoelectric element that is advantageous for increasing reliability and reducing size. A piezoelectric vibrating gyrosensor utilizes a phenomenon in which a Coriolis force occurs perpendicularly to vibrations when an angular velocity is applied to a vibrating object.
For example, a vibrating gyrosensor which detects an angular velocity causes a physical quantity transducer (vibrator) to produce driving vibrations in a specific direction. When an angular velocity is applied to the vibrator, a Coriolis force occurs perpendicularly to driving vibrations to produce detection vibrations. Since the detection vibrations occur perpendicularly to the driving vibrations, a detection signal (signal component due to detection vibrations) differs in phase from a drive signal (signal component due to driving vibrations) by 90 degrees. The detection signal can be synchronously detected separately from the drive signal utilizing the above phenomenon, for example.
A vibrating gyrosensor is used in a wide variety of applications, such as shake detection for a video camera or a digital camera, positioning using the global positioning system (GPS) for a car navigation system, and aircraft or robot position detection.
A vibrating gyrosensor used in these applications is driven by a battery. Therefore, it is necessary to increase the life of the battery by reducing the power consumption of the vibrating gyrosensor as much as possible. In this case, it is preferable to stop supplying power to the vibrating gyrosensor when an angular velocity or the like is not detected and to supply power to the vibrating gyrosensor from the battery only when using the vibrating gyrosensor. This makes it necessary to cause the vibrating gyrosensor to perform a normal operation within a short period of time after activation.
It is important to reliably cause a vibrating gyrosensor to start an operation which implements steady oscillations by causing current to flow through an oscillation loop during oscillation startup. Specifically, an oscillation driver circuit does not necessarily start the operation which implements steady oscillations even when activating the oscillation driver circuit by supplying power. There may be a case where current does not flow through the oscillation loop even after supplying power, whereby steady oscillations do not occur even after a certain period of time. The reliability of a physical quantity measuring device is increased by preventing such a situation (i.e., oscillation failure).
JP-A-2004-286503 discloses technology which reduces the startup time of a vibrating gyrosensor, for example. JP-A-2004-286503 discloses technology in which a CR oscillation circuit or a ring oscillator is provided in an oscillation loop so that the oscillation amplitude is increased by an amplifier immediately after activation.
A driver device of a vibrating gyrosensor must cause a vibrator to constantly vibrate (oscillate) at its resonance frequency in order to stably detect the angular velocity applied to the vibrator. The driver device also must cause the vibrator to oscillate within a short time to start a normal operation. Moreover, it is preferable to form the driver device using a small circuit with low power consumption in order to increase the life of a battery at low cost.
On the other hand, when forming the vibrator using a crystal with a high Q value and hermetically sealing the vibrator in a package, the driving Q value of the vibrator increases to a large extent. Therefore, the period of time (startup time) until a signal from the vibrator becomes stable increases when causing the vibrator to produce driving vibrations.
According to the technology disclosed in JP-A-2004-286503, when causing the crystal vibrator to oscillate at a frequency close to its driving frequency, the areas of a capacitor and a resistor of the CR oscillation circuit must be increased. This results in an increase in size and cost of a vibrating gyroscope (vibrating gyrosensor). According to the technology disclosed in JP-A-2004-286503, it is difficult to cause the crystal vibrator with a high Q value to operate at its driving frequency because the crystal vibrator is driven at another frequency during startup. Therefore, the period of time until stable oscillations are achieved increases when affected by manufacturing variations and the like.
According to the technology disclosed in JP-A-2004-286503, signal energy from the CR oscillation circuit or the like is injected into the vibrator irrespective of whether or not the vibrator oscillates. In this case, since energy is injected at a specific frequency regardless of the resonance frequency of the vibrator, the signal from the CR oscillation circuit hinders steady oscillations when the vibrator produces steady oscillations. Therefore, in order to reduce the startup time required for the vibrator to produce steady oscillations, it is necessary to inject energy into the oscillation loop so that the oscillations of the vibrator are not hindered due to an oscillation condition which differs to a large extent from the steady oscillation condition of the oscillation loop including the vibrator.